Intubation is a common requirement for anaesthesia, and a laryngoscope is a commonly used instrument for visualizing the larynx to allow the introduction of an endotracheal (ET) tube. The view obtained at laryngoscopy is normally graded on a 1–4 scale, depending on to what extent the view is obscured. Grades 1 and 2 usually provide little difficulty with intubation. However a grade 3 larynx can present considerable difficulty, often requiring special techniques such as blind insertion of the ET tube. A grade 4 larynx is often impossible to intubate using a standard laryngoscope and normally requires the use of more specialized equipment such as fiberoptic equipment. There are four main anatomical factors that contribute to confound the view of the larynx, namely, forward displacement of the larynx, forward or prominent upper teeth, backward displacement of the tongue and poor mouth opening. Another major factor that contributes to confound the view is the inability to achieve what is commonly known as the Magill position of neck flexion and head extension due to either cervical spine instability or pathological disease such as rheumatoid conditions or ankylosing spondylitis.
In its basic form, a laryngoscope includes a handle with a slightly curved or straight plate, commonly known as a blade, extending substantially perpendicularly from the handle. The Macintosh laryngoscope, which normally has a slightly curved blade, is an example of such a laryngoscope, In use, the blade is inserted into the patient's mouth until its tip is located at the base of the patient's tongue, Normally the tip of the blade is positioned between the base of the person's tongue and the epiglottis such that, by lifting the laryngoscope anteriorly, the tongue and epiglottis are moved allowing a clearer view of the trachea. A user will generally look for the larynx (vocal cords) which gives, an exact indication of the position in which to place the breathing tube.
The use of a curved Macintosh blade laryngoscope in the context of a Grade 3 or 4 larynx may necessitate a forward and upward levering movement. In such situations the patient's teeth may inadvertently be used as a fulcrum and persistent attempts to elevate the epiglottis frequently results in damage to the upper teeth. In an attempt to overcome this problem, a levering laryngoscope, commonly known as the McCoy laryngoscope, was created. The McCoy laryngoscope has a pivotable tip at the end of the blade, the tip being operable by a lever on the handle of the laryngoscope. When the handle is depressed, the tip pivots to pull the epiglottis away from the mouth of the larynx. The McCoy laryngoscope helps to improve the view of the larynx and, because the fulcrum point is at the distal end of the blade, decreases the likelihood of the patient's teeth being damaged.
It is also known to provide the blade with a deployable mirror which, during use, allows the user to view the larynx more clearly. U.S. Pat. No. 6,135,948 (Lee) describes an example of such a laryngoscope. However, the Lee Laryngoscope is considered to be awkward to use.
Despite the devices described above, intubation remains difficult in many cases. It would be desirable, therefore, to provide an improved laryngoscope, particularly since prolonged attempts at laryngoscopy often result in injury, most commonly vocal cord haematoma and mucosal lacerations.